Process for recovery of amino acids from aqueous mixtures

ABSTRACT

Disclosed is a process for recovery of amino acids from aqueous mixtures. In particular, it relates to a treatment of said amino acid containing aqueous mixture prior to extraction of the amino acid with a water immiscible organic solution containing a water insoluble extractant for said amino acid. The overall process of the invention which includes the pretreatment and extraction, also includes optional methods of recovering said extracted amino acid from the water immiscible organic solution. Accordingly, the invention also relates to a process for recovery of the amino acid by stripping of the amino acid from the organic solution and precipitation of the amino acid.

This application is a division, of application Ser. No. 864,064, filed05/16/86 now U.S. Pat. No. 4,886,889.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for recovery of amino acids fromaqueous mixtures. In particular, it relates to a treatment of said aminoacid containing aqueous mixture prior to extraction of the amino acidwith a water immiscible organic solution containing a water insolubleextractant for said amino acid. The overall process of the inventionwhich includes the pretreatment and extraction, also includes optionalmethods of recovering said extracted amino acid from the waterimmiscible organic solution. Accordingly, this invention also relates toa process for recovery of the amino acid by stripping of the amino acidfrom the organic solution.

2. Description of Related Art

Amino acids, essential to animal and human nutrition are important asfood additives, feed supplements, artificial sweeteners, and intravenoussolutions; thus production and purification of amino acids is animportant procedure. Descriptively, amino acids are organic acidscontaining an amino group. These compounds can be obtained by hydrolysisof a protein, by organic synthesis, or by fermentation. As a generalrule., all naturally occurring amino acids are alpha-amino acids, havingthe --NH₂ group attached to the carbon atom next to the COOH group,beta-alanine being an exception to this generalization. Some amino acidsare termed essential meaning that they are required for an organism'sgrowth, but can not be synthesized by its body. Essential amino acidsfor human beings are: arginine, histidine, isoleucine, leucine, lysine,methionine, phenylalanine, threonine, tryptophan, and valine.

Due to present industrial procedures, it is necessary to remove aminoacids from dilute fermentation broths and other aqueous mixtures.Current methods used to remove and purify amino acids arecrystallization, chromatography, ion-exchange, and extraction. One suchmethod, described in U.S. Pat. No. 2,894,954 teaches that amino acidscan be removed as a solute in N-hexylamine by a plurality ofliquid/liquid contacting zones. In accordance with this method theN-hexylamine is then separated from the amino acids.

Another extraction method used to separate amino acids from fermentationbroths and other aqueous mixtures is discussed in: "Quantitativedeterminations by ion pair extraction", ACLA PHARM. SNEC. 12, 407-416(1975), by Thomas Nordgren, and Rolf Modine which teaches the extractionof amino acids from fermentation broths by combining a water solubleextractant, tetrapentylammoniumiodide with an aqueous phase containingamino acids, and subsequently washing with methylene chloride. Thismethod, disadvantageously has a tendency to leave water soluble ionpairs formed by the combination of extractant and amino acid in theaqueous phase, which are not extracted in the organic phase.

Another extraction method of recovering amino acids from aqueousmixtures is commonly assigned co-pending U.S. Pat. Application Ser. No.617,767, filed Jun. 6, 1984, by Tuominen et al now U.S. Pat. No.4,661,606. In this Application is disclosed a process for extraction ofamino acids from aqueous solutions containing at least one amino acidwith a solution of a water insoluble extractant in a water immiscibleorganic solution. Two phases are formed, an organic phase containing theextracted amino acid and an aqueous phase, containing the non-amino acidmaterials. The two phases which are immiscible are then separated andthe amino acid is then recovered from the organic phase. The amino acidis recovered either by precipitation or stripping from the organicsolution into a second aqueous solution from which the amino acid can berecovered by conventional purification methods.

A method of isolating L-dopa from aqueous solutions thereof employing asulfonic acid as a liquid ion exchanger can be seen in U.S. Pat. No.3,928,431. In this method however, sulfonic acids such as dodecylbenzenesulfonic acid, a water soluble surfactant is employed. Such material isalso disclosed as a surfactant in European Patent Publication No. 73381.

Such European Patent Publication further describes several aqueousmixtures containing amino acids, which are obtained during thefermentative production of amino acids. As set forth therein, referenceis made to "Chem. Abstr. 76, P 57 722k; 78, P 122655y; 78, R 146 210a;82, P 15274j and 85, P 121 806f), L-tyrosine (see, for example, Chem.Abstr. 76, P 84 566n; 77, P 60 057y; 78, R 146 210a; 82, P 17 199 m and85, P121 806f), 3-hydroxy-L-tyrosine =DOPA (see, for example, Chem.Abstr. 76, P 152 037z; 78, P 157 879b; 80, 144 375a; 81, P 3 699f and83, P 7 116q), L-tryptophane (see, for example, Chem. Abstr. 78, P 56436z, R 146 220d; 81, P 13 463m; 84, 15 655a) and5-hydroxy-L-tryptophane (see, for example, Chem. Abstr. 76, P 139 064m;79, P 103 669; 80. P 13 649v; 80, P 106 876g and 83, 106 65s). It isbasically possible to extract the actual aqueous microorganism culturesthus obtained, but it is usually more advantageous to filter orcentrifuge these before extracting and to further process the solutionsobtained.

BRIEF DESCRIPTION

This invention has several aspects to an overall process which includes

(A) a pretreatment process prior to extraction;

(B) extraction of the amino acid with an organic solution; and

(C) a process of recovery of the amino acid from the organic extractantsolution.

The pretreatment process prior to extraction involves either or both oftwo treatments or processes:

(a) an ultrafiltration and/or

(b) an adsorption treatment.

The preferred treatment is an ultrafiltration employing a membranehaving a molecular weight cut off high enough to permit passage of theamino acids, but low enough to prevent passage of cellular materials,tars, other solids, etc. The amino acid can then be recovered from thediffusate by extraction with an appropriate extractant, as described incommonly assigned, co-pending Application Serial No. 617,767 notedearlier above. In this process an amino acid containing aqueoussolution, such as an amino acid fermentation broth (such as those notedin EP Publication No. 73881), is placed on one side of an appropriatemembrane having the desired pore size, with water (i.e. deionized water)or other appropriate liquid media employed as the diffusate on the otherside of the membrane. After a time sufficient for the amino acid todiffuse through the membrane, the diffusate may then be contacted with awater insoluble extractant in a water immiscible organic solution.Instead of employing water as a diffusate media, diffusion andextraction may be concurrent by the use of the organic solutioncontaining the extractant as the diffusate media. Thus, the amino aciddiffuses through the membrane into the organic extractant solution fromwhich the amino acid can then be recovered.

The membrane ultrafiltration may be conducted using any membraneconfiguration, including flat sheet, spiral wound, hollow fiber, ortubular membranes. The flat sheet can be employed in a batch treatmentprocess; it may also be employed in a continuous process where the flatsheet is fixed or spiral wound. These membranes are generally employedin continuous processes wherein the feed material (such as afermentation broth containing the amino acid) flows parallel to themembrane surface and the amino acid permeates or diffuses through thepores of the membrane to the permeate or diffuse side. The flow of fluidis adjusted, so as to minimize fouling of the membrane resulting in areduction of the amino acid permeating through the membrane.

This ultrafiltration process may be defined as a process of separatingamino acids from an aqueous solution or suspension containing desiredamino acid, cells, and undesired materials, comprising bringing saidaqueous suspension into contact with one side or surface of a chemicallyresistant membrane, said membrane having micropores of a size sufficientfor said amino acids to pass through, diffuse or permeate to the otherside of said membrane. In ultrafiltration said membrane has microporesof a mean diameter less than about 0.2 micron, or a molecular weightcutoff of about 300,000.

Another process of treating said amino acid containing aqueoussuspension is to bring said aqueous suspension into contact with afinely divided clay, clay like material, activated carbon or lime, whichwill adsorb at least a portion of the undesirable materials, andseparating said finely divided materials and adsorbed undesirablematerials from the remaining aqueous solution or suspension containingsaid amino acid. This treatment may be followed by the ultrafiltrationprocess discussed immediately above or may be preceded by theultrafiltration.

Either treatment tends to remove surfactant materials from the aqueoussuspension, the presence of which tends to cause problems in phasedisengagement in any subsequent extraction process employing a waterimmiscible organic solution containing a water insoluble extractant.

The extraction step with the water immiscible organic solution is asdisclosed in commonly assigned co-pending Application Ser. No. 17,767,noted earlier, the disclosure of which is incorporated herein byreference.

After the extraction, the amino acid is found loaded into the organicphase from which the amino acid must be recovered. In Serial No.617,767, the amino acid is stripped from the organic phase either by theuse of a gaseous stripping agent or aqueous stripping agent. With agaseous salt forming agent, a precipitate is formed and the precipitatedamino acid salt is removed by conventional filtration methods. With anaqueous stripping agent the amino acid is released from the organicphase and transferred into the aqueous stripping phase from which theamino acid is then recovered by conventional means.

The present invention further encompasses other methods or processes ofstripping or recovering the amino acid from the organic phase. One ofthe most preferred methods is stripping the loaded organic phase bycontacting said organic phase with a concentrated acid, such as 85% H₂SO₄, in an amount sufficient to precipitate the amino acid. The aminoacid under these conditions is insoluble in the organic phase and noidentifiable aqueous phase results and the amino acid precipitates. Inthe absence of any aqueous phase, the process has the advantage of easyseparation of the solid, precipitated amino acid from the liquid organicphase in contrast to a three phase system as described below.

Another adaptation of this recovery method is one in which the loadedorganic phase is contacted with an aqueous solution already saturatedwith the amino acid, after which the sulfuric acid is added. The aminoacid is insoluble in the organic and since the aqueous phase is alreadysaturated also, the amino acid is also insoluble in the aqueous phaseand precipitates. The amino acid may also be released from the organicextractant by use of an acidic aqueous stripping solution from which theamino acid is recovered by precipitation after the separation from theorganic phase. In a cationic extractant system, the acidic strippingsolution is added to provide one or more equivalents of acidic protonsbased on the amino acid in the organic solution. If one equivalent ofacidic proton is used, the neutral amino acid is obtained; if more thanone equivalent is used, either the salt or the neutral amino acid isobtained. About one equivalent, is most preferred. For anionicextraction systems, the acidic stripping solution is added to provideone extra equivalent of acidic protons and the precipitate is the aminoacid salt.

There are two adaptations of this release of amino acid from the organicextractant solution resulting in transfer of the amino acid into anaqueous solution using aqueous acid solutions wherein the amino acidprecipitates. These are based on two properties of the amino acid,particularly phenylalanine, which facilitates isolation from the aqueousstripping solution. The properties include increasing water solubilitywith increasing temperatures and increasing water solubility withdecreasing pH below that at the isoelectric point.

The process based on temperature dependent solubility is conducted bystripping at an elevated temperature with an aqueous solution containingone equivalent of acidic protons based on the amino acid, such asphenylalanine, in the organic solution. The released phenylalanine istransferred into the aqueous solution at the pH at the isoelectricpoint, separated from the organic phase, and, if the process isconducted to effect sufficient concentration, the neutral amino acidprecipitates when the aqueous solution is cooled.

The process based on pH dependent solubility can be conducted at anyconvenient temperature by stripping with an aqueous solution containingexcess acid. Phenylalanine is released from the extractant andtransferred into an aqueous solution at a pH below that at theisoelectric point. If the process is conducted to effect sufficientconcentration, the neutral amino acid can be precipitated by adjustingthe pH of the solution to that at the isoelectric point with a suitablebase. Suitable bases for pH adjustment are the alkali metal hydroxides,ammonia or ammonium hydroxide. Suitable acids for stripping for both thetemperature dependent and pH dependent process include the mono-, di-and triprotic acids with anions including the halides, N₀₃, C10₄, BF₄,PF₆, SO₄ and PO₄.

In still another variation of stripping from amino acid a loadedcationic extractant organic solution, the loaded organic is contactedwith a brine at a pH greater than or equal to that at the isoelectricpoint. The amino acid is displaced from the extractant and transferredinto the aqueous solution, from which it is precipitated.

The amino acid, such as phenylalanine, can be isolated from the aqueoussolution as a neutral solid when the stripping process is conducted toprovide sufficient concentration. If the pH of the brine is near that atthe isoelectric point, stripping at an elevated temperature will providea solution from which phenylalanine will precipitate upon cooling. Ifthe pH of the brine is greater than that at the isoelectric point,stripping at any convenient temperature will provide a solution fromwhich phenylalanine will precipitate upon adjustment of the pH to thatat the isoelectric point.

Useful brines are solutions of salts for which the anion has someaffinity for the cationic extractant. Examples include the alkali metaland alkaline earth metal halides and nitrates. The concentration of thebrine solution should be such that substantial stripping is obtained.Thus, the higher the affinity of the anion for the cationic extractant,the lower the required concentration. Concentrations between 5 w/w% andsaturation are useful. The pH of the brine solution can be adjusted toor above that at the isoelectric point with an alkali metal hydroxide.

In the preferred system, the concentration of phenylalanine orphenylalanate in the strip solutions should be >20 g/l to affordadequate recovery. There should be at least a 20° C. temperaturedifferential between the stripping temperature and the precipitationtemperature for the temperature dependent precipitation. Suitable acidsfor pH adjustment in the pH dependent precipitation include mono-, di-and triprotic acids with anions, including the halides, SO₄, NO₃, Cl0₄,BF₄, PO₄ and PF₆. The most useful acids, however, are those containingthe same anion as that of the salt used in the brine.

Accordingly, one aspect of the invention includes a method of strippingan organic extractant solution containing an amino acid comprisingcontacting said organic extractant solution with an aqueous strippingsolution and precipitating said amino acid.

DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS

As indicated earlier, the present invention involves an overall processwhich includes

(A) a pretreatment process prior to extraction

(B) extraction of the amino acid with an organic solution, and

(C) a process for recovery of the amino acid from the organic extractantsolution.

The preferred pretreatment is an ultrafiltration employing a membranehaving a molecular weight cut off high enough to permit passage of theamino acids, but low enough to prevent passage of other undesirablematerials in the fermentation broth being treated.

The process is useful with fermentation broths containing at least oneamino acid. It is particularly useful for the processing of lysine,phenylalanine or tryptophan fermentation broths. Generally these brothshave already had the cellular material removed by conventionalfiltration, or other method, prior to treatment in accordance with thepresent invention, however, there may still be some cellular materialpresent. The fermentation broths to which the invention is particularlyapplicable are those containing the desired amino acid (in typicalconcentrations above 1% to about 5%) and further composed as follows:

    ______________________________________                                        Insoluble Component                                                                             Soluble Component                                           ______________________________________                                        (a) Microorganisms    (x)   Soluble Non-Utilized Raw                                                      materials                                         (b) Non-Utilized Raw Materials                                                                      (y)   Soluble Metabolites                               (c) Insoluble Salts   (1)   Polysaccharides and sugars                        (d) Immiscible Oils   (2)   Proteins and Amino Acids                          (e) Insoluble Metabolites                                                                           (3)   Lipids                                                                  (4)   Nucleic Acids                                     ______________________________________                                    

Membranes employed in the process, whether flat sheet, spiral wound,tubular or hollow fiber, are a wide variety of semi-permeable orpermselective ultrafiltration membranes, which are effective to rejectmolecules having a molecular weight of over 300,000. The membrane may bedescribed as "a semi-permeable membrane capable of concentrating aminoacids", which term as used herein means a membrane system capable ofrejecting molecules over 300,000 molecular weight. The membrane willhave micropores permitting passage of the desired amino acid on theorder of about 0.001 to about 0.2 microns, or a molecular weight rangeup to about 300,000. The preferred range nominal molecular weight cutoff(NMWC) is about 1000-100,000 molecular weight.

The materials from which the membrane are made are of a wide varietywell known to those skilled in the membrane art. The more typicalpreferred materials, for example, cellulose acetate type; polysulfone,polyamide, fluoropolymers, polyolefinic polymers such as polypropylene.The material, of course, must be inert under conditions of use and thematerials being treated. Membranes of polysulfone type are particularlyuseful in the present invention in treating amino acid containingfermentation broths.

In a typical cross flow ultrafiltration employing spiral wound, tubularor hollow fiber membrane, the fermentation broth flows parallel to thewall or surface of the membrane. The amino acid permeates or diffusestransverse to the membrane through the membrane to the permeate side ofthe membrane. The cross flow of the fermentation broth past the membraneis adjusted so as to minimize any deposition of undesired materials onthe membrane, which tend to clog or foul the membrane and reduce theefficiency of the filtration. When the membrane is clogged, backflushingis needed to remove membrane fouling. The membrane is generally as thinas possible in order to avoid pressure drop across the membrane.

As indicated in the brief description an alternative treatment of thefermentation broth may be considered in lieu of the ultrafiltration,such as an adsorption treatment. This adsorption treatment may also beemployed in combination with the ultrafiltration step, either before orafter the ultrafiltration. Treatment prior to ultrafiltration ispreferred, as it may minimize any problems with the ultrafiltration andparticularly minimize the necessity for backwashing.

In this adsorption step, the fermentation broth is contacted with afinely divided material such as a clay or clay like material, activatedcarbon or lime. The particular treatment, whether ultrafiltration oradsorption or combination thereof, will large depend on the quality ofthe fermentation broth and components found therein. Both the adsorptiontreatment or the ultrafiltration remove materials which behave assurfactants which can cause problems in the subsequent extraction step,where good phase disengagement is desirable. Any surfactant present willtend to promote some emulsification with attendant phase disengagementproblems.

The adsorbants which are utilized are commercially available materials.In general, all of the common, commercial crystalline clay minerals maybe used such as the montmorillonite, kaolinite, hectorite andattapulgite. As a generality, clays vary considerably in compositiondepending upon the locality of the deposit. The preferred clays are thecommercial bentonite clays which contain sufficient montmorillonite,such as 75%. Commercially available clays of this type are acid pH (acidactivated) clays such as Filtrol Grade 1.

In the adsorption treatment, the fermentation broth is intimately mixedwith the adsorbent and then filtered to remove the adsorbent and anyother solids. After the adsorption treatment, the filtrate may then besubject to an ultrafiltration if such seems indicated. Generally, theadsorption step will be sufficient in itself and no ultrafiltration isnecessary. Conversely, if ultrafiltration is employed, there isgenerally no need for the adsorbent treatment.

After the pretreatment of the broth, either by adsorption,ultrafiltration, or both, the aqueous broth containing the amino acid isthen subjected to extraction employing a water insoluble extractant insolution in a water immiscible organic solvent. As indicated earlier,this extraction is conducted in accordance with commonly assigned,co-pending U.S. Pat. application Ser. No. 617,767, the disclosure ofwhich was incorporated herein by reference, and which reference shouldbe made for details contained therein. A brief discussion of the generalextraction technique however follows.

Generally, amino acids can be extracted from aqueous solutions by aprocess comprising contacting an aqueous mixture containing amino acidswith a water immiscible organic solution containing a water insolubleextractant, thereby forming two phases and separating the two phasesafter amino acids have transferred into the organic phase. With theadsorption or ultrafiltration treatment discussed earlier, phasedisengagement of the two phases is clear, sharp and rapid.

While a number of extractants are disclosed in the commonly assignedApplication, the preferred extractants are certain quaternary ammoniumcompounds (cationic) or certain organic sulfonic acids (anionic). Thequaternary ammonium compounds are those of the formula ##STR1## whereR₁, R₂, R₃ and R₄ individually are aliphatic hydrocarbon groupscontaining from about 1 to about 22 carbon atoms and where R₁, R₂, R₃and R₄ together have a minimum of 25 carbon atoms, and where at leastthree groups selected from the group consisting of R₁, R₂, R₃ and R₄ areat least a C₄.

Suitable sulfonic acid extractants are those having the formula ##STR2##where R₅ and R₆ are aliphatic hydrocarbon groups individually with fromabout 6 to about 22 carbon atoms, where R₅ and R₆ together contain atleast 18 carbon atoms, and where neither R₅ nor R₆ are smaller than aC_(6;) and organic sulfonic acids having the structural formula:##STR3## where R₇ and R₈ are aliphatic hydrocarbon groups containingfrom about 4 to about 22 carbon atoms, where R₇, R₈, or the sulfonicgroup may be attached to positions 1-8 on the aromatic rings, and whereneither R₇ nor R₈ is smaller than a C₄, and where R₇ and R₈ togetherhave at least 18 carbon atoms.

These extractants are not only essentially water insoluble, but aresoluble in non-polar water immiscible organic solvents. When theseextractants are dissolved in the non-polar solvent, amino acids areextracted from the immiscible aqueous (polar) phase that it is contactedwith.

The quaternary ammonium compounds and sulfonic acids defined above arewell known and commonly recognized by those in the extraction art.Further, such compounds are commercially available or are easilyprepared by known methods. The quaternary ammonium compounds arecationic extractants soluble in water immiscible organic solvents.Illustrative of such are found in U.S. Pats. Nos. 3,455,816; 4,128,493;3,215,620 and 3,215,621. Commercially available quaternary compounds arealso disclosed in General Technical Bulletin 12-A-2 of General Mills, ofJanuary 1966 entitled "Fatty Nitrogen Chemicals for Industry", whichdescribe "ALIQUAT®" quaternary ammonium compounds containing mono-, di-and trifatty alkyl groups.

The sulfonic acids defined above are anionic extractants and are alsowell known compounds either available commercially or can be made byconventional, known technology. U.S. Patent 4,160,0807, which makesreference to sulfonic acids from which the patentee prepares his desiredsulfonamido oximes.

In order to be extracted in accordance with the process of the instantinvention, the amino acid being removed from the aqueous mixture mustnot be in its zwitterion form. This zwitterion is that form of an aminoacid where the amino acid molecule contains both a positive and negativecharge. This form, which will vary slightly with the specific amino acidin solution, occurs in an aqueous solution over the more neutral pHranges (from about 4.5 to 7.5). To extract amino acids therefore, theinstant invention generally requires the aqueous mixture containingamino acids to have an acidic pH value of about 4.5 or less (preferablyless than 3.0), or a basic pH value of about 7.5 or more so that theamino acids are predominately not zwitterions. Alternatively stated, theamino acids must be in an aqueous (polar) phase having a pH such thatthe amino acids are either cationic or anionic.

Acid or base can be added to the aqueous mixture in order to maintainthe pH at the right level. Suitable acids to be used for pH control inthe aqueous mixture are mineral acids, and suitable bases to be used arealkali and alkali earth metal hydroxide and ammonium hydroxide bases.The stronger acids and bases which tend to be soluble in water andinsoluble in the organic phase are preferred; such acids arehydrochloric, hydrofluoric, nitric, sulfuric, hydrobromic andphosphoric. Phosphoric acid is a good acidifying agent for the aqueousphase. Suitable bases for pH control in the aqueous phase include alkalimetal or alkaline earth metal bases, particularly potassium hydroxide,sodium hydroxide, ammonium hydroxide and sodium carbonate.

General extractions of overall amino acids from fermentation broths andother aqueous mixtures can also be accomplished. In this instance anoverall and substantially complete removal of amino acids from theaqueous mixture is desired. Acceptably, the ratio of extractantconcentration to amino acid concentration is 1:1 on a molar basis.Preferably, the ratio should be from about 1.2 moles of extractant peramino acid molar concentration, to about 10 moles of extractant pertotal moles of amino acid. However, the concentration of extractant canbe limited to less than 1 mole per mole of amino acids in order toextract more preferentially one amino acid over another. Thus, the ratioof the number of moles of extractant in the organic solution to thenumber of moles of amino acids in the aqueous solution will generally bein the range of from about 0.25-10 moles of extractant per mole of aminoacid, more desirably a molar ratio of 1:1 to 2:1.

The respective volumes of the phases are generally determined byindividual need, such as the type of extraction system used, and therespective concentrations of the solutions. Since amino acids mustfrequently be extracted from very dilute aqueous solutions, the organicto aqueous volume ratio can acceptably vary from about 1:20 to about20:1. More desirably, a more effective range for the ratio of theorganic phase volume to the aqueous phase volume is from about 1:5(organic to aqueous) to about 5:1 (organic to aqueous). A more preferredratio for the organic phase volume to the aqueous phase volume,especially in commercial extraction systems is from about 1:3 to about3:1.

The organic extractant phase should contact the aqueous amino acid phasefor a sufficient length of time to permit the amino acids to enter theorganic phase. The time of contact depends on the particular system, thetype of equipment used, and upon individual needs and desires. As ageneral rule, however, the contact time between the organic extractantsolution and the aqueous amino acid mixture should be in excess of 0.1seconds with some equipment, but generally less than 3 hours. Naturallya minimum contact time is desired, thus a more desirable phase contacttime would be in the range of from about 5 seconds to one hour while amore preferred contact time is from about 5 seconds to about 10 minutes.

Any substantially water immiscible liquid solvent can be used in theprocess of the instant invention. Typically, this includes aliphatic andaromatic hydrocarbons. Aliphatic hydrocarbons such as alkanes, includingcycloalkanes and halogenated alkanes are suitable; preferred alkaneshave a minimum of five carbon atoms; preferred halogenated alkanes havea minimum of two carbon atoms; aromatic hydrocarbons which can be usedinclude benzene, and substituted products such as toluenes, xylenes andcumene. Also suitable as a solvent are those esters, ethers, ketones,and alcohols which are substantially water immiscible. Furthermore anyblend of these substances or a water immiscible kerosene is alsosuitable. Preferred organic solvents for use in the amino acid recoveryprocesses are the aliphatic and aromatic hydrocarbons having flashpoints of 150° F. and higher and solubilities in water of less than 0.1%by weight. These solvents are also essentially non-toxic and chemicallyinert and the costs thereof are currently within practical range.Representative commercially available solvents are: Kermac 470B (analiphatic kerosene available from Kerr-McGee-Flash Point 175° F.),Chevron Ion Exchange Solvent (available from Standard Oil ofCalifornia - Flash Point 195° F.), Escaid 100 and 110 (available fromExxon-Europe - Flash Point ≈180° F.), Norpar 12 (available fromExxon-U.S.A. - Flash Point 160° F.), Conoco C-1214L (available fromConoco - Flash Point 160° F.), Aromatic 150 (an aromatic keroseneavailable from Exxon-U.S.A. - Flash Point 150° F.) and various otherkerosenes and petroleum fractions available from other oil companies.

Modifiers can be added to the solvent in addition to the extractant inorder to modify or improve the extraction of amino acids. Substances,which are preferred as modifiers are alcohols in the range of from about10 to about 13 carbon atoms and phenols such as the alkyl (8-12 carbonatom) substituted phenols, can be added to improve solubility, phaseseparation and/or other important characteristics of the organicsolution.

The extraction process is preferably conducted in a countercurrentcontinuous process, but may be conducted in a batch process. Generally,the extraction is conducted employing one extractant and at one pHlevel. However, a two stage extraction process may be employed, in whichan extraction is conducted in a first pass at a low pH, followed byextraction at a higher pH. Such a process will generally employ aquaternary ammonium extractant of the type described earlier. In anyevent, the extraction process provides an organic solution of theextractant, which contains the amino acid from which the amino acid mustbe removed and recovered. In the commonly assigned, co-pendingapplication noted earlier, this removal was carried out

(a) using an acid or basic gas to precipitate the amino acid from theorganic solution; or

(b) contacting the organic solution phase with an aqueous strippingsolution, whereby the amino acid is transferred from the waterimmiscible organic solution into the aqueous stripping solution.

In the latter, two phases which are immiscible are provided, which canthen be separated. The organic phase is then returned to the circuit forextraction and the aqueous phase now containing the amino acid in higherconcentration is treated by any conventional method, such asprecipitation, crystallization and the like to recover the amino acid.

In the present invention, other methods were found by which the aminoacid can be removed from the organic phase. Thus, the present inventionis concerned with an improved method of removal of amino acid from waterimmiscible organic solutions of a water insoluble extractant containingan amino acid. In each of these, an aqueous stripping solution isemployed and the amino acid is precipitated, in which form it can berecovered in solid form by simple filtration or separation technique.The removal of the amino acid from the organic solution may be carriedout in any of four different variations described below:

(a) contacting the organic solution containing the amino acid with aconcentrated acid solution, such as 85% sulfuric acid, in an amount toprecipitate the amino acid, in the absence of any aqueous phase;

(b) contacting the organic solution containing the amino acid with anaqueous acidic solution saturated with the amino acid whereby the aminoacid precipitates being insoluble in the organic and the aqueous phases;

(c) contacting the organic solution containing the amino acid with anaqueous acidic solution, whereby the amino acid is transferred to theaqueous acidic phase, which is separated from the organic phase, andprecipitating the amino acid from the aqueous phase by adjusting thetemperature or the pH level so as to precipitate the amino acid;

(d) contacting the organic solution containing the amino acid with abrine at a pH greater than or equal to that at the isoelectric pointwhereby the amino acid is displaced from the extractant in the organicsolution and transferred to the aqueous solution.

In variation (a) above, the amino acid is precipitated from the organicextractant solution containing the amino acid by contacting the waterimmiscible organic solution with a concentrated acid solution in anamount sufficient to precipitate the amino acid. Concentrated acidsolutions of acids, such as sulfuric acid, phosphoric acid, hydrohalidesuch as hydrochloric or hydrobromic, tetrafluoroboric,hexafluorophosphoric, nitric, trifluoroacetic and oxalic arerepresentative of those which are employed.

In variation (b), the same acids noted in (a) may be employed. In thevariation, three phases are present:

(1) the organic phase

(2) aqueous phase saturated with the amino acid; and

(3) a solid amino acid phase.

The solid phase may be removed by filtration or centrifugation leavingthe two immiscible organic and aqueous phases, which can be separatedand recycled for use in the circuit.

In variation (c), the amino acids are released from the extractant andtransferred into an aqueous solution using aqueous acid strippingsolutions.

For cationic extractant systems, the acidic stripping solution is addedto provide one or more equivalents of acidic protons based on amino acidin the organic solution, If one equivalent of acidic protons is used,the neutral amino acid is obtained; if more than one equivalent is used,either the salt or the neutral amino acid is obtained. For anionicextractant systems, the acidic stripping solution is added to provideone extra equivalent of acidic protons and the precipitate is the aminoacid salt.

Two properties of the amino acid facilitate its isolation from theaqueous stripping solutions. The properties include increasing watersolubility with increasing temperature and increasing water solubilitywith decreasing pH below that at the isoelectric point.

The process based on temperature dependent solubility is conducted bystripping at an elevated temperature with an aqueous solution containingone equivalent of acidic protons based on the amino acid in the organicsolution. The released amino acid is transferred into the aqueoussolution at the pH at isoelectric point, which is separated from theorganic phase and, if the process is conducted to effect sufficientconcentration, the neutral amino acid precipitates when the aqueoussolution is cooled. The preferred process would be conducted with aleast a 20° C. differential between stripping temperature andprecipitation temperature and the concentration of phenylalanine in thestrip solution before cooling would be >20 g/l. Suitable acids for suchstripping include mono-, di and triprotic acid with anions including thehalides, NO₃, Clo₄, BF₄, PF₆, SO₄ and PO₄.

The process based on pH dependent solubility can be conducted at anyconvenient temperature by stripping with an aqueous solution containingexcess acid. The amino acid is released from the extractant andtransferred into an aqueous solution at a pH below that at theisoelectric point. If the process is conducted to effect sufficientconcentration, the neutral amino acid can be precipitated by adjustingthe pH of the solution to that at the isoelectric point with a suitablebase. In the preferred process, the amount of acid in the strippingsolutions would be at least a two-fold molar excess based onphenylalanine and the concentration of phenylalanine in the stripsolution before pH adjustment would be >20 g/l. Suitable acids are thesame as described for the temperature dependent process. Suitable basesfor pH adjustment are the alkali metal hydroxides.

Variation (d) is particularly useful in removing or stripping the aminoacid from loaded cationic extractant organic solutions. In thisvariation, the loaded organic is contacted with a brine at a pH greaterthan or equal to that at the isoelectric point and the amino acid isdisplaced from the extractant and transferred into the aqueous solution.

The amino acid, particularly phenylalanine, can be isolated from theaqueous solution as a neutral solid when the stripping process isconducted to provide sufficient concentration. If the pH of the brine isnear that at the isoelectric point, stripping at an elevated temperaturewill provide a solution from which the amino acid will precipitate uponcooling. If the pH of the brine is greater than that at the isoelectricpoint, stripping at any convenient temperature will provide a solutionfrom which the amino acid will precipitate upon adjustment of the pH tothat at the isoelectric point.

Useful brines are solutions of salts for which the anion has someaffinity for the cationic extractant. Examples include the alkali metal(such as Na or K) and alkaline earth metal (such as Ca and M9) halidesand nitrates. The concentration of the brine solution should be suchthat substantial stripping is obtained. Thus, the higher the affinity ofthe anion for the cationic extractant, the lower the requiredconcentration. Concentrations between 5 w/w% and saturation are useful.The pH of the brine solution can be adjusted to or above that at theisoelectric point with a base such as an alkali metal or alkaline earthmetal hydroxide, ammonium hydroxide, sodium carbonate and the like.

In the preferred system, with phenylalanine, the concentration ofphenylalanine or phenylalanate in the strip solutions should be >20 g/lto afford adequate recovery. There should be at least a 20° C.temperature differential between the stripping temperature and theprecipitation temperature for the temperature dependent precipitation.Suitable acids for pH adjustment in the pH dependent precipitationinclude mono-, di- and triprotic acids with anions, including thehalides, SO₄, NO₃, Cl0₄, BF₄ and PF₆. The most useful acids, however,are those containing the same anion as that of the salt used in thebrine.

The following examples serve to illustrate, but not limit, theinvention. All parts and percentages are by weight, unless otherwisenoted.

In the examples, the fermentation broths used were a phenylalanine(hereinafter PHE) and a lysine (hereinafter LYS) fermentation brothtypically containing about 3% amino acid. Otherwise, chemicals andequipment used were as follows:

    ______________________________________                                        Chemical or Equipment                                                                            Available From                                             ______________________________________                                        Methyltricaprylammonium                                                                          Henkel Corporation                                         Chloride (ALIQUAT ® 336)                                                  Dinonylnaphthalene Sulfonic Acid                                                                 King Industries                                            Decalin (cis, trans-decahydro-                                                                   E. I. duPont de Nemours &                                  naphthalene)       Co.                                                        Low-Aromatic Kerosene                                                                            Exxon Chemicals                                            (ESCAID 110)                                                                  Tridecyl Alcohol   Exxon Chemicals                                            1,2-Dichloroethane Aldrich Chemicals                                          Clay (Filtrol Grade 1)                                                                           Filtrol                                                    Activated Carbon (Norit A)                                                                       Matheson Coleman & Bell                                    Lime (CaO)         Matheson Coleman & Bell                                    Cross flow Filtration Membranes                                                                  Millipore Corporation                                      Dialysis Membrane Tubing                                                                         Spectrum Medical Industries                                ______________________________________                                    

In the examples, the quaternary ammonium sulfate organic extractantsolution was prepared by dissolving methyltricaprylammonium chloride(135 g/l) and tridecyl alcohol (150 g/l) in decalin or low-aromatickerosene and washing the resulting solution with several one volumeportions of aqueous sodium sulfate (100 g/l). The sulfonic acid organicextractant solution was prepared by dissolving dinonylnaphthalenesulfonic acid (150 g/l) in 1,2-dichloroethane.

PART I BROTH PRETREATMENT Example 1

This example is a control to illustrate the phase disengagementtypically required when no adsorbent or ultrafiltration was employed.Using only simple filtration of the PHE fermentation broth to removeinsolubles, the pH was adjusted to pH 11 by adding 50% sodium hydroxideand the sample was filtered. Phase disengagement was assessed by shakingthe sample (1.0 part) and quaternary ammonium sulfate organic extractantsolution (1.0 part) together for 10 minutes and transferring the mixtureto a separatory funnel. Phase disengagement typically required between15 minutes and 24 hours. The resulting mixtures typically containedlarge amounts of insoluble material at the interface.

A. Adsorbent Treatment Examples Example 2

PHE fermentation broth (100 parts) was stirred vigorously with clay (1part) for 30 minutes and the mixture was filtered. Phase disengagementwas assessed as described in Example 1 and less than 5 minutes wasrequired to give a mixture with clean, well-defined interface.

Example 3

PHE fermentation broth (100 parts) was stirred vigorously with activatedcarbon (1 part) for 30 minutes and the mixture was filtered. Phasedisengagement was assessed as described in Example 1 and less than 5minutes was required to give a mixture with a clean, well-definedinterface.

Example 4

PHE fermentation broth (100 parts) was stirred vigorously with lime (1part) for 30 minutes and the mixture was filtered. Phase disengagementwas assessed as described in Example 1 and less than 10 minutes wasrequired to give a mixture with only a small amount of insolublematerial at the interface.

B. Ultrafiltration Treatment Examples Example 5

A series of experiments was conducted in which PHE fermentation brothwas filtered in a cross flow mode using commercially availablefiltration equipment. PHE fermentation broth was prefiltered to removeinsolubles and cross flow filtered. The filtration was continued until aspecified percentage of the feed had been collected as filtrate. Intwo-stage filtration experiments, the retentate was then diluted to aspecified volume with deionized water and the filtration process wasrepeated until a second specified percentage had been collected asfiltrate. The two filtrates were combined. In five-stage filtrationexperiments, dilution of retentate and filtration was repeated fourtimes after the first filtration. Phase disengagement was assessed inall cases as described in Example 1. The results are given in Table Ibelow.

                                      TABLE I                                     __________________________________________________________________________    Membrane                                                                            Number of                                                                           % First                                                                            Retentate                                                                          % Subsequent                                                                          Phase                                           NMWC  Stages                                                                              Filtrate                                                                           Dilution                                                                           Filtrates                                                                             Disengagement*                                  __________________________________________________________________________     1,000                                                                              2     60   1.5  60      A                                                10,000                                                                             5     90   1.0  50      A                                                30,000                                                                             2     80   4.0  70      B                                               100,000                                                                             5     90   1.0  50      B                                               300,000                                                                             1     90   --   --      B                                               __________________________________________________________________________     *A = Phase Disengagement within 5 minutes to give a mixture with clean,       welldefined interface;                                                        B = Phase Disengagement within 5 minutes to give a mixture with a small       amount of insoluble material at the interface                            

Example 6

PHE fermentation broth was filtered to remove insolubles. The sample wassealed in dialysis membrane tubing (nominal molecular weight cutoff≈1,000) and immersed in an equal volume of deionized water with stirringfor 16 hours. Phase disengagement was assessed as described in Example 1and less than 5 minutes was required to give a mixture with a clean,well-defined interface.

Example 7

A sample of LYS fermentation broth was filtered to remove insolubles.The sample (1.0 part) was diluted with deionized water (1.0 part) andthe pH was adjusted to pH 1.4 by adding sulfuric acid. Phasedisengagement was assessed by shaking the sample (1.0 part) and sulfonicacid organic extractant solution (1.0 part) together for 5 minutes in aseparatory funnel. Phase disengagement required 2 to 3 hours.

Example 8

LYS fermentation broth (1.0 part) was sealed in dialysis membrane tubing(nominal molecular weight cutoff ≈1,000) and immersed in deionized water(4.0 parts) with stirring for 6 hours. The pH of the permeate wasadjusted to pH 1.4 by adding sulfuric acid and phase disengagement wasassessed as described in Example 8. Phase disengagement required 30minutes.

PART II STRIPPING

In these examples, the chemicals and equipment were as specified abovein Part I. In these examples, the loaded organic extractant solution wasprepared by:

(1) shaking a sample of quaternary ammonium sulfate organic extractantsolution (1.0 part) with PHE fermentation broth, which was cross flowfiltered (nominal molecular weight cutoff of 10,000) and subsequentlyadjusted to pH 11 (1.0 part) for 10 to 15 minutes and separating thephases; or

(2) countercurrent extraction of PHE from cross flow filtered PHEfermentation broth (10,000 nominal molecular weight cutoff) andsubsequently adjusted to pH 11 with quaternary ammonium sulfate organicextraction solution at a phase ratio of 1:1 in a one-inch York-Scheibelextraction column.

Example 9

A series of experiments was conducted in which the concentration of asulfuric acid stripping solution was varied (mol H⁺ /PHE ≈1.0). The PHEloaded organic was placed in a beaker with a magnetic stirring bar andthe stripping solution was added with vigorous stirring. Precipitateformed immediately. Stirring was continued for 30-45 minutes and thesolid was isolated by filtration or centrifugation, washed with hexaneand air-dried. The results of the experiments are given in Table IIbelow in which no aqueous phase was present at concentrations of 25 to100.

                  TABLE II                                                        ______________________________________                                        H.sub.2 SO.sub.4                                                                              % PHE Recovered To                                            Concentration   Solid     Organic                                             ______________________________________                                        100             76        22                                                  85              86        17                                                  77              75        20                                                  50              76        23                                                  25              81        19                                                  10               70*       25*                                                 5              .sup. 60.sup.+                                                                          .sup. 22.sup.+                                      ______________________________________                                         *1% PHE recovered to aqueous phase                                            .sup.+ 7% PHE recovered to aqueous phase                                 

Example 10

A series of experiments was conducted in which the mole ratio of acidicprotons to PHE in the loaded organic was varied (mole H⁺ /PHE ≈0.4-2.4). The PHE loaded organic was placed in a beaker with a magneticstirring bar and the sulfuric acid stripping solution (85% H₂ SO₄) wasadded with vigorous stirring. Precipitate formed immediately. Stirringwas continued for 30-45 minutes and the solid was isolated by filtrationor centrifugation, washed with hexane and air-dried. The results of theexperiments are given in Table III below.

                  TABLE III                                                       ______________________________________                                        Mole         % PHE Recovered To                                               Ratio        Solid     Organic                                                ______________________________________                                        0.4          18        86                                                     0.8          50        57                                                     1.0          86        17                                                     1.2          86        27                                                     1.6          89        22                                                     2.0          90        22                                                     2.4          77        12                                                     ______________________________________                                    

Example 11

PHE loaded organic (1.53% PHE, 330 parts) was placed in a beaker with amagnetic stirring bar and phosphoric acid (85%, 1.0 part) was added withvigorous stirring. Precipitate formed within 1 minute. Stirring wascontinued for 30-45 minutes and the solid was isolated by filtration,washed with hexane and air-dried. Recovery of PHE to solid was 55% andto stripped organic was 58%.

Example 12

PHE loaded organic (1.53% PHE, 120 parts) was placed in a beaker with amagnetic stirring bar and hydrochloric acid (38%, 1.0 part) was addedwith vigorous stirring. Precipitate formed with 1 minute. Stirring wascontinued for 30-45 minutes and the solid was isolated by filtration,washed with hexane and air-dried. Recovery of PHE to solid was 54% andto stripped organic was 44%.

Example 13

A sample of quaternary ammonium sulfate organic extractant solution (1.0part) was contacted with three successive portions of a solution oftryptophan (2.0 parts) at pH 12.5. The loaded organic contained 5.1%tryptophan. Loaded organic (130 parts) was placed in a beaker with amagnetic stirring bar and the sulfuric acid stripping solution (85% H₂SO₄, 1.0 part) was added with vigorous stirring. Precipitate formedimmediately. Stirring was continued for 30 minutes and the mixture wascooled at 0° C. for 16 hours. The solid was isolated by filtration orcentrifugation, washed with hexane and air-dried. Recovery of tryptophanto solid was 79%.

In Examples 14 and 15 below, the organic extractant solution consistedof ALIQUAT®336 (45 g/l) and tridecyl alcohol (50 g/l) in decalin. Theorganic solution (200 ml) was contacted successively with three equalvolumes of a ph 12.5 solution of phenylalanine (25 g/l) in deionizedwater. The loaded organic solution was filtered to remove entrainedaqueous. The resulting solution typically contained 14 g/l.

Example 14

A mixture of loaded organic extractant solution (200 ml) and 20%hydrochloric acid (100 ml) was shaken vigorously for 30 minutes. Thelayers were separated and the pH of the aqueous layer was adjusted to pH5.9±0.1 using 45% sodium hydroxide. After cooling to 0° C., a whitesolid precipitated. The solid was isolated by filtration and washed withhexanes (2×50 ml). The solid was identified as neutral phenylalanine byinfrared and NMR. The recovery of solid phenylalanine in stripping was35.7%. The filtrate contained phenylalanine at 17.6 g/l.

Example 15

The loaded organic extractant solution (200 ml) was stirred vigorouslyand 85 w/w % aqueous sulfuric acid (1.0 g) was added. A white solidprecipitated immediately upon addition. The mixture was cooled to 0° C.,the precipitated solid was isolated by filtration and washed with hexane(2×50 ml). The recovery in the stripping step is >95% and the solid wasneutral phenylalanine by infrared analysis.

Example 16

A stripping solution was prepared by adding sulfuric acid (85%, 1.0part) to a solution of PHE in deionized water (3.00% PHE, 250 parts).The stripping solution was added to PHE loaded organic (1.57% PHE, 250parts) in a beaker with vigorous stirring. The mixture was stirred for30 minutes, allowed to stand for 1 hour and filtered to isolate theprecipitate PHE. The recovery of PHE as solid was 54%. The strippedorganic contained 0.34% PHE and the aqueous phase contained 3.31% PHE.

Example 17

This example illustrates the use of a brine. A 210 ml portion of anorganic solution consisting of ALIQUAT®336 (45 g/l) and tridecyl alcohol(50 g/l) in decalin was contacted successively with three 200 mlportions of a pH 12.5 solution of phenylalanine (25 g/l) in deionizedwater. The loaded organic was filtered to remove entrained aqueous. Theresulting solution typically contained 14 g/l phenylalanine.

The striping solution consisted of sodium chloride (200 g/l) indeionized water. Sodium hydroxide (45%) was added to raise the pH to pH12.5 The loaded organic was contacted with a 70 ml portion of thestripping solution. The resulting brine solution contained 32 g/lphenylalanine. The brine solution was warmed to ≠35° C. and the pH wasadjusted to pH 5.9±0.1 using concentrated hydrochloric acid. The mixturewas cooled to 0° C, the solid was isolated by filtration and washed withhexanes (2×50 ml). The filtered brine contained 2.5 g/l phenylalanineand the solid was 3.2 g of phenylalanine. The identity of the productwas confirmed by infrared spectroscopy.

We claim:
 1. A process of recovering an amino acid from a waterimmiscible organic solvent solution of a water insoluble quaternaryammonium extractant containing said amino acid comprising contactingsaid organic solvent solution with a concentrated acid solution wherebyno separate aqueous phase forms, and whereby said amino acid is strippedfrom said quaternary ammonium extractant and precipitated from saidorganic solvent solution in the absence of a separate aqueous phase. 2.A process as defined in claim 1 wherein said concentrated acid is 85%sulfuric acid.
 3. A process as defined in claim 1 wherein saidconcentrated acid is 38% hydrochloric acid.
 4. A process as defined inclaim 1 wherein said acid is 85% phosphoric acid.
 5. A process asdefined in claim 1 wherein said organic solvent is selected from thegroup consisting of water immiscible aliphatic and aromatic hydrocarbonsand said quaternary ammonium has the cation of the formula: ##STR4##where R₁, R₂, R₃ and R₄ individually are aliphatic hydrocarbon groupscontaining from about 1 to about 22 carbon atoms and where R₁, R₂, R₃and R₄ together have a minimum of 25 carbon atoms and where at leastthree groups selected from R₁, R₂, R₃ and R₄ are at least a C₄.
 6. Aprocess as defined in claim 5 in which said organic solvent is keroseneand said quaternary ammonium compound is methyl tricaprylyl ammoniumchloride.
 7. A process of recovering an amino acid from a waterimmiscible organic solvent solution of a water insoluble quaternaryammonium extractant containing said amino acid comprising contactingsaid organic solvent solution with an aqueous stripping solutionsaturated with said amino acid to which from about 1 or more equivalentsof acidic proton is added, thereby forming an aqueous phase and anorganic phase in which phases said amino acid is insoluble whereby saidamino acid precipitates.
 8. In a process as defined in claim 7 whereinsaid quaternary ammonium extractant has a cation of the formula:##STR5## where R₁, R₂, R₃ and R₄ individually are aliphatic hydrocarbongroups containing from about 1 to about 22 carbon atoms and where R₁,R₂, R₃ and R₄ together have a minimum of 25 carbon atoms and where atleast three groups selected from R₁, R₂, R₃ and R₄ are at least a C₄ andabout 1 equivalent of acidic proton per equivalent of amino acid isadded whereby the neutral amino acid is precipitated.
 9. In a process asdefined in claim 7 wherein said quaternary ammonium extractant has thecation of the formula: ##STR6## where R₁, R₂, R₃ and R₄ individually arealiphatic hydrocarbon groups containing from about 1 to about 22 carbonatoms and where R₁, R₂, R₃ and R₄ together have a minimum of 25 carbonatoms and where at least three groups selected from R₁, R₂, R₃ and R₄are at least a C₄.
 10. In a process as defined in claim 7 wherein saidquaternary ammonium extractant is methyl tricaprylyl quaternary ammoniumchloride, said organic solvent is kerosene, and more than 1 equivalentof acidic proton is added whereby the salt or neutral amino acid isprecipitated.
 11. A process of recovering an amino acid from a waterimmiscible organic solvent solution of a water insoluble quaternaryammonium extractant containing said amino acid comprising contactingsaid organic solvent solution with an aqueous acidic stripping solutioncontaining about one equivalent or more of acidic proton based on theamino acid in said organic solution at a first temperature whereby saidamino acid is transferred from said organic solution into said aqueousstripping solution at a pH at the isoelectric point, separating theorganic solvent solution phase from the aqueous stripping solution phaseand reducing the temperature at least 20° C. below the first strippingtemperature whereby said amino acid precipitates.
 12. A process ofrecovering an amino acid from a water immiscible organic solventsolution of a water insoluble quaternary ammonium extractant containingsaid amino acid comprising contacting said organic solvent solution withan aqueous acidic stripping solution containing a molar excess of acidbased on said amino acid whereby said amino acid is transferred fromsaid organic solvent solution into said aqueous stripping solution at apH below the isoelectric point, separating the organic solvent solutionphase from the aqueous stripping solution phase and adjusting the pH ofsaid aqueous stripping solution to the isoelectric point whereby saidamino acid precipitates.
 13. A process of recovering an amino acid froma water immiscible organic solvent solution of a water insolublequaternary ammonium extractant containing said amino acid comprisingcontacting said organic solvent solution with a brine at a pH greaterthan or equal to the isoelectric point whereby said amino acid istransferred from said organic solvent extractant solution into saidbrine and precipitating said amino acid from said brine.
 14. A processas defined in claim 13 wherein the pH of said brine is at theisoelectric point and said amino acid is precipitated by reducing thetemperature by at least 20° C. below the stripping temperature.
 15. Aprocess as defined in claim 13 wherein the pH of said brine is greaterthan the isoelectric point and said amino acid is precipitated byadjusting the pH to the isoelectric point.